Subject:
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RCX has a fast clock, was Re: Rolling ball clock revisited
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Newsgroups:
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lugnet.technic, lugnet.robotics
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Date:
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Wed, 8 Dec 2004 09:31:25 GMT
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Viewed:
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167 times
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Hello dave,
> It was interesting to read this bit off your website--
>
> "
> The problem should have been very simple: each minute, start the elevator
> until a ball is detected by one sensor. Unfortunately, my first try over a
> several hours period showed me that my clock was fast, several seconds each
> hour! After eliminating all mechanical possibilities (two balls at a time, or
> an undetected ball), I concluded that my RCX itself was fast... To make sure,
> I finally put a frequency meter probe on RCX crystal, and indeed it
> oscillates at 16.03 MHz instead of 16.00 MHz. So I finally added some code to
> wait for 6.92 seconds each hour. "
>
> This explains much to me--I have an 1.0 AC'd RCX that's been on for months
> but almost weekly I have to reset the clock. Thanks for the info on the fast
> clock!
A made an experiment this night using a RCX 2.0, the clock was fast by about 10s
per hour.
I suppose that this problem comes from bad capacitor loading of the crystal used
on RCX. Crystals need to see some capacitance to oscillate at the right
frequency, generally in the 10 to 30pF range. Even if PCB traces themselves
bring some capacitance, there is no added caps on RCX PCBs (see
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=38746), this should be enough to
explain the problem.
Philo
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Message has 1 Reply:
Message is in Reply To:
 | | Re: Rolling ball clock revisited
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| (...) I love it! Very nicely done! It was interesting to read this bit off your website-- " The problem should have been very simple: each minute, start the elevator until a ball is detected by one sensor. Unfortunately, my first try over a several (...) (20 years ago, 7-Dec-04, to lugnet.technic, lugnet.robotics, FTX)
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